The bypass loop to a pressure reducing valve should always be designed such that the safety valve and moisture separator is always in line of the steam delivery line.
It is well recognized in the plant engineering teams that reducing the steam pressure to a figure sufficient to meet the process temperature requirements reduces steam consumption. Therefore, pressure reducing valves (PRV) have become a commonplace across process plants. A safety valve is placed after the PRV to ensure high pressure steam doesn’t accidentally reach the process equipment in case of PRV failure.
A moisture separator is also recommended before the PRV to ensure dry steam reached the PRV as well as the process.
In cases where the PRV and its accessories are fabricated by local fabricators especially for Non IBR lines, it is found that the bypass provided completely bypasses this entire set up . In this scenario, whenever the PRV will be bypassed the process equipments will receive wet steam at the full pressure as the moisture separator, strainer and safety valve will not be in-line with the steam delivery line for the process equipments. This is a major safety hazard.
The recommended PRV setup is where the moisture separator and safety valve are always in-line of the steam delivery line to the process equipments . This ensures that under all scenarios the process equipments are always protected by the Safety Valve and moisture separator. Equipments providers for long have provided pre-fabricated Pressure Reducing Stations with all the accessories installed in the right place.